A belt press normally comprises vertically spaced upper and lower traverses, each normally formed by a plurality of parallel profiled beams extending perpendicular to the direction of the belt passing through the press, and respective upper and lower platens carried by these upper and lower traverses. Each platen in turn is formed by a press plate that directly engages the belt being pressed and by an actuating member that urges the press plate away from the respective traverse to force it against the belt being pressed. Links are provided rigidly interconnecting the outer ends of the upper and lower traverses, which normally deform away from each other during the pressing operation.
The actuating member for such a system is normally fluid operated and comprises a simple bladder or cushion that is braced between the traverse and the respective press plate of each platen. Since the traverses do not present continuous support surfaces, it is standard practice to laminate to this cushion at least one plate that engages the respective traverses. Such a bladder or cushion, which replaces the hitherto used piston-and-cylinder arrangements, is then pressurized pneumatically or hydraulically for operation of the press.
Although the use of such a cushion or bladder does give considerable advantages over the standard piston-and-cylinder systems, the assembly is still relatively expensive. The laminating of reinforcing plates to the bladder considerably increases the cost of the system. Furthermore, as heaters are provided on the press plates, it is necessary to make the bladder of expensive heat-resistant material, or carefully to insulate the bladder.